DEVELOPMENTT OF THE OSTRICH FERX. 41 



anastomose to some extent, making the distribution of the pits or young sieve-discs 

 irregular. As they become older these thickened bands become more strongly marked, 

 but the thickenings are uniform, so that the sieve-discs do not present a bordered appear- 

 ance, although sometimes, owing apparently to a slight rounding of the outer surface 

 of the thickened ridges, the outline of the sieve-disc is not as clearly defined as when 

 the breadth of the band is absolutely uniform. Corresponding thickenings are formed 

 on the opposite sides of the wall, and probably fine pores are developed in the lateral 

 sieve-plates, but this could not be proved. In one case, an oblique wall, which separates 

 the ends of two neighboring tubes, and was very strongly inclined, shoAved several very 

 sharply defined pits, which appeared to penetrate the wall and thus to throw the cavities 

 of the adjoining tubes into communication. The complete tubes are seldom perfectly 

 straight, the lateral walls being curved, especially at points where the bundle is bent. 



The remaining procambium undergoes little change, retaining the form of thin-walled 

 parenchyma occupying the spaces between the tracheids and outside of the sieve-tubes. 

 Two or three rows remain, forming a ring inside the bundle-sheath which ditters from 

 them mainly in the walls of its cells being brown, and the cells flattened laterally. As 

 the tracheids become old, their Avails often become yellow. 



The complete rhizome is comparatively slender, being only about two centimetres in 

 diameter; but, on account of the persistent bases of the petioles, it appears much thicker, 

 often ten centimetres or more. These overlapping leaf-bases give it a bulb-like appear- 

 ance, as those of several years remain attached. The rhizome is either upright or in- 

 clined at the base, and may reach a length of twenty to thirty centimetres, or even more 

 in old plants. The oblanceolate leaf-bases are about four centimetres long by one cen- 

 timetre in breadth and one-half centimetre thick. They project above the j^oung leaves 

 and thus jM-otect them before they are ready to unfold. 



With a little care, portions of the net-like, fibro-vascular cylinder of the stem can l)e 

 sepai-ated, as like the bimdles of the leaves, it is sharply ditterentiated and readily comes 

 away from the surrounding jjarench^ina. The bundles are firm and Avoody in texture 

 and the meshes of the net nearly rhombic, about one-half centimetre in length. From 

 the loAver angle of each mesh, tAvo bundles, one on each side, are sent to the leaf, there 

 being a leaf opposite each foliar gap. 



LeloAV the leaf-bundles, or sometimes connected Avith them, the bundles of the roots 

 join the stem-bundle, there being usually in the older parts several roots at the base of 

 each leaf. There are no bundles running tln-ough the medulla. 



Connected with the rhizome there are usually to be found numerous long and slender 

 stolons, Avhich under faA'oi'able circumstances appear above ground and develop a crown 

 of leaves. 



They arise near the bases of the leaves, and in almost any plant numbers may be met 

 Avith ranging in size from one-half centimetre in length to tAventy or thirty centimetres 

 or more, and apparently remaining dormant for an indefinite period, as the number of un- 

 deATdoped ones fiir exceeds those wliich have groAAai to the surface of the ground. A 

 section through the base shoAvs a single axial bundle Avhich is connected Avith the bundle 

 of the rhizome close to the base of a leaf The stem of the stolon remains for a long- 

 time slender, and the narrow scale-leaves, Avhich shoAV no division into stalk and blade 



MLMOIKS KOSrON SOC. NAT. HIST., VOL. IV. 



